1. Field of the Invention
The present invention relates to a method of forming a hole for an interlayer connection conductor, a method of producing a resin substrate and a component-incorporated substrate, and a resin substrate and a component-incorporated substrate.
2. Description of the Related Art
A component-incorporated substrate in which a mount component is embedded inside a resin layer is lightweight and does not require burning at a high temperature as is the case with a ceramic multi-layer substrate, such that there are very few restrictions on the mount component to be incorporated therein. Therefore, such a component-incorporated substrate can be used in a wide variety of applications in the future. However, ways to improve the quality and to reduce the cost thereof are problematic.
FIG. 7C illustrates a conventional component-incorporated substrate 40. In FIG. 7C, the component-incorporated substrate 40 includes a core substrate 41 having a top surface with an in-plane electrode 42 provided therein, a mount component 44 mounted on the in-plane electrode 42 with a bonding material 43, and a resin layer 45 arranged to cover the top surface of the core substrate 41 and the mount component 44. An interlayer connection conductor 48 is arranged in the resin layer 45 to electrically connect the in-plane electrode 42 to external.
FIGS. 7A, 7B and 7C illustrate a method of producing the conventional component-incorporated substrate 40. FIG. 7A shows a state before the formation of a hole for an interlayer connection conductor, and FIG. 7B shows a state after the formation of a hole for an interlayer connection conductor 47 in the resin layer 45. The hole for the interlayer connection conductor 47 is formed by removing the resin layer 45 on the in-plane electrode 42 by laser machining. By filling the hole for the interlayer connection conductor 47 with a conductive paste, the interlayer connection conductor 48 shown in FIG. 7C is formed.
However, in the conventional production method as described above, a situation arises in that when the hole for the interlayer connection conductor 47 is formed by laser machining, the in-plane electrode 42 disposed beneath the hole for the interlayer connection conductor 47 is also removed. This is related to the surface roughness of the in-plane electrode 42. After removal of the resin layer 45 by laser machining, a laser beam reaches the surface of the in-plane electrode 42, wherein the in-plane electrode 42 is removed by the laser beam which is not reflected, if the surface roughness of the in-plane electrode 42 is relatively rough and the reflectivity of the laser beam is reduced accordingly. Even when the surface of the in-plane electrode 42 is relatively smooth, damage caused by the laser beam is likely to occur if the in-plane electrode 42 is relatively thin. When a portion of the in-plane electrode 42 is removed and damaged, the connection with the interlayer connection conductor 48 is insufficient, and a quality problem arises.
Machining with a laser having a reduced energy so that the laser beam will not damage the in-plane electrode 42 has been considered. However, when the laser energy is reduced, the machining time to remove the resin layer 45 is increased. This increases the cost, especially when a component-incorporated substrate having a large number of holes for the interlayer connection conductor 47 is produced.
Accordingly, a method of producing a component-incorporated substrate which ensures a sufficient connection between an in-plane electrode and an interlayer connection conductor at a reduced cost has been demanded.
Japanese Unexamined Patent Publication No. 6-314884 describes another example of the related art. Japanese Unexamined Patent Publication No. 6-314884 discloses a method of providing a hole for an interlayer connection conductor without performing laser removing machining by laminating a resin layer having a hole disposed therein so as to eliminate the aforementioned problem.
However, when this method is used to produce a component-incorporated substrate, resin flow corresponding to the volume of the mount component occurs during the lamination of the resin layer, such that the hole for the interlayer connection conductor is likely to deform. Therefore, the method disclosed in Japanese Unexamined Patent Publication No. 6-314884 is not suited for producing a component-incorporated substrate having a mount component incorporated therein.